MATLAB Function Reference (Volume 2: Graphics)

imageWhen you write an indexed image using imwrite, MATLAB automaticallyconverts the values if necessary.ColormapsColormaps in MATLAB are alway m-by-3 arrays of double-precisionfloating-point numbers in the range [0, 1]. In most graphics file formats,colormaps are stored as integers, but MATLAB does not support colormapswith integer values. imread and imwrite automatically convert colormapvalues when reading and writing files.True Color ImagesIn a truecolor image of class double, the data values are floating-pointnumbers in the range [0, 1]. In a truecolor image of class uint8, the data valuesare integers in the range [0, 255] and for truecolor image of class uint16 thedata values are integers in the range [0, 65535]If you want to convert a truecolor image from one data type to the other, youmust rescale the data. For example, this statement converts a uint8 truecolorimage to double,RGB64 = double(RGB8)/255;or for uint16 images,RGB64 = double(RGB16)/65535;This statement converts a double truecolor image to uint8.RGB8 = uint8(round(RGB64*255));or for uint16 images,RGB16 = uint16(round(RGB64*65535));The order of the operations must be as shown in these examples, because youcannot perform mathematical operations on uint8 or uint16 arrays.When you write a truecolor image using imwrite, MATLAB automaticallyconverts the values if necessary.ObjectHierarchy2-231